There is technically no such thing as “tornado season.” A tornado can happen during any month of the year. As I write this on the morning of March 1st (the beginning of meteorological Spring), this period of time is also associated with a seasonal uptick in severe weather activity across parts of the United States. This Spring, scientists will engage in a new field campaign called PERILS (Propagation, Evolution, and Rotation in Linear Storms). What is that and why is it important?
Mobile radars will be critical to the PERILS campaign.
Before I get into what PERILS is, let’s discuss field campaigns. As a scientist, I am very familiar with their purpose, but many of you probably are not. Field campaigns are coordinated, long-term observational programs that provide specialized measurements in order to evaluate hypotheses, gather unique data, test models, and refine understanding of scientific processes. A press release issued by the National Oceanic and Atmospheric Administration (NOAA) National Severe Storms Laboratory (NSSL) says the goal of PERILS is, “to characterize the near-storm environments and internal storm processes associated with tornado-producing quasi-linear convective systems (QLCSs) and other non-classical tornadic storms in areas spanning from the Missouri bootheel southward to the Gulf Coast and from the mid- and lower-Mississippi Valley eastward to the foothills of the Appalachian Mountains.” It will be one of the largest severe weather campaigns in history and will extend through 2023. For a complete overview of the various components, click this link.
A classic supercell
Some of the terminology in that quote from the press release may have been unfamiliar to the average person so let’s break it down. Many tornadoes emerge from supercell thunderstorms, which are characterized by a rotating updraft (mesocyclone). As compared to other types of thunderstorms, they are the least common but can be associated with violent weather such as tornadoes, hail, and destructive winds. They can be long-lasting, which is what we witnessed in the long-track tornadoes in the South-Mid-South region at the end of 2021.
A Quasi-Linear Convective System on weather radar
Other types of cloud systems can also spawn tornadoes. Quasi-linear convective systems (QLCSs) are thunderstorms oriented in a linear fashion. Because of strong winds in the system, they can also have bulges or “bows” when observed on a weather radar (animation above) or satellite imagery. According to NSSL’s website, “Nearly 20% of all tornadoes are associated with lines of strong thunderstorms called “quasi-linear convective systems” (QLCS).” Though often shorter-lived and weaker than supercell thunderstorms, they are particularly dangerous for a couple of reasons. They can spawn tornadoes and often happen at night or during early morning hours. They are also common in the South, which has more obstructing trees or terrain than the Great Plains and a large percentage of socio-economically vulnerable communities.
Study region for PERILS
PERILS is an opportunity to learn more about QLCS and other non-supercell tornadoes (landspouts and waterspouts) in the South. It is a partnership between NOAA and several universities. It is also something else that deserves highlighting -science that the public doesn’t see but may ultimately lead to better life-saving forecasts. Your smartphone, heart medication, or GPS system didn’t materialize out of thin air (poof). It takes research and development efforts like PERILS.
If you see funny-looking trucks this Spring in your community, it may be the PERILS storm chasers.
